Resistance of thermally modified ash (Fraxinus excelsior L.) wood under steam pressure against rot fungi, soil-inhabiting micro-organisms and termites

Abstract

Thermal modification processes have been developed to increase the biological durability and dimensional stability of wood. The aim of this paper was to study the influence of ThermoWood Ò treatment intensity on improvement of wood decay resistance against soil-inhabiting microorganisms , brown/white rots and termite exposures. All of the tests were carried out in the laboratory with two different complementary research materials. The main research material consisted of ash (Fraxinus excelsior L.) wood thermally modified at temperatures of 170, 200, 215 and 228°C. The reference materials were untreated ash and beech wood for decay resistance tests, untreated ash wood for soil bed tests and untreated ash, beech and pine wood for termite resistance tests. An agar block test was used to determine the resistance to two brown-rot and two white-rot fungi according to CEN/TS 15083-1 directives. Durability against soil-inhabiting microorganisms was determined following the CEN/TS 15083-2 directives, by measuring the weight loss, modulus of elasticity (MOE) and modulus of rupture (MOR) after incubation periods of 24, 32 and 90 weeks. Finally, Reticulitermes santonensis species was used for determining the termite attack resistance by non-choice screening tests, with a size sample adjustment according to EN 117 standard directives on control samples and on samples which have previously been exposed to soil bed test. Thermal modification increased the biological durability of all samples. However, high thermal modification temperature above 215°C, represented by a wood mass loss (ML%) due to thermal degradation of 20%, was needed to reach resistance against decay comparable with the durability classes of ''durable'' or ''very durable'' in the soil bed test. The brown-rot and white-rot tests gave slightly better durability classes than the soil bed test. Whatever the heat treatment conditions are, thermally modified ash wood was not efficient against termite attack neither before nor after soft rot degradation.

Effect of thermal treatment on physical and mechanical properties of birch and pine wood

“…The present research is a part of the investigation aimed at improving wood bio-durability by combined wood thermal treatment and impregnation with a commercial biocide. It is found that substantial enhancement of bio-durability can only be reached by wood thermal treatment at the temperature range at which wood mechanical strength significantly decreases consequently restricting the application area of the material (Kamdem, Pizzi, & Jermannaud, 2002;Metsä-Korteleinen & Viitanen, 2010;Candelier et al, 2017). It is expected that by applying the proposed combined treatment process a material with decent mechanical strength and meeting the requirements of the use class 3 according to the EN 335-1 standard will be obtained.…”

Moisture-Dependent Strength Properties of Thermally-Modified Fraxinus excelsior Wood in Compression

“…The treatment significantly improves its performance making it suitable for different uses. In respect to biological effectiveness, studies have shown that heat treatment considerably enhances ash resistance to brown-and white-rot fungi and soil-inhabiting microorganisms (for heat treatment at a temperature >200 • C) [19]. However, it is not effective against thermites [19,20].…”

“…In respect to biological effectiveness, studies have shown that heat treatment considerably enhances ash resistance to brown-and white-rot fungi and soil-inhabiting microorganisms (for heat treatment at a temperature >200 • C) [19]. However, it is not effective against thermites [19,20]. Thermal modification reduces the equilibrium moisture content (EMC) of ash [3,21,22] and decreases its water retention value [23], enhancing its dimensional stability [22,24,25].…”

Chemical composition as factor affecting the mechanical properties of thermally modified black poplar (Populus nigra L.)

“…The temperature of the modification process plays a crucial role for the final effect and should be adjusted for the species of wood. Usually, thermal modification of wood is carried out between 160 and 230 °C (Majano-Majano et al 2012;Oliver-Villanueva et al 2013;Shchupakivskyy et al 2014;Zauer et al 2014;Sandak et al 2015;Candelier et al 2017).…”